My motherboard has 2 USB 3.o slots in the back, where the usual slots go, but the tower also supports 1 or 2 USB 3.0 ports in the front, above the DVD drive. So, there is a cord coming out of those ports that has an end exactly like the one in the attached picture. I am not able to find a matching port on the mobo, so I presume it doesn't have one, and I would need an adapter or else just leave it inoperable. I have an ASUS P8Z68-V LX and an Antec 900 tower.

There are only two USB 3.0 ports (the blue ones at the back), and the other 12 (black) are USB 2.0.

That board seems to be something of a "value" board because a space for the connector in question does exist, but is not actually implemented. You can see where it should be on your board in the highlighted area in figure 1 and where it is implemented on a similar, but "deluxe" version of your motherboard in the highlighted area in figure 2 (the photos are scaled down; open them in a new tab to see them full-size).

You have two other options:

Get an extension cable and plug it into the blue port(s) at the back. They can be had on eBay for a couple of dollars.

Try to find a USB 3.0 male header to female plug adapter. Unfortunately, most adapters tend to be female on the header end, or male on the plug end.

If you want to use the header on your case, you'll have to buy an expansion card to connect it. Silverstone makes one that's currently ~$23 on Amazon. You'd plug your cases table into the black header and a 4 pin Molex power connector from your PSU into the white one.